Public bug reported:
Hello,
I attempt to attach the Ctrl+Alt+Delete keyboard shortcut to the 'Log
Out' window by opening the Keyboard Shortcuts applet and assigning
<Control><Alt>Delete to the 'Log out' entry. I then close the Keyboard
Shortcuts window to ensure that this new hot key is activated (although
this should not be necessary).
If I then press Ctrl+Alt+Delete (ensuring that I use the left Alt key),
no Log Out window appears. I tried assigning Shift+4 to this action
with no success. I can replicate this behaviour on two different
machines.
If I minimise all windows, select an icon on the desktop and then press
the designated hot key, the selected icon flashes; this suggests that at
least something is happening.
** Affects: control-center (Ubuntu)
Importance: Undecided
Status: Confirmed
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System > Quit does not respond to assigned keyboard shortcut/hotkey
https://launchpad.net/bugs/71620